Increase Total Alkalinity
• Add 1 kg sodium bicarbonate per 10,000 L of pool water to increase the total alkalinity by 50 ppm.
Decrease Total Alkalinity
• Dilution of pool water will lower alkalinity in most situations. If consistently high total alkalinity is creating problems, expert advice should be sought on the choice of disinfectant and pH correction chemicals.
• Before adjusting pH, ensure the total alkalinity is appropriate and stable.
• Add 100 mL of hydrochloric (muriatic) acid or 120 g of sodium bisulphate (dry acid) per 10,000 L of pool water for a decrease in pH by approximately 0.1–0.3. Always dilute the acid in fresh water before adding it to the pool.
• No more than 100 mL of hydrochloric acid or 120 g of sodium bisulphate should be added at once. Otherwise, the pH may be lowered dramatically.
• The pH should be retested after a turnover period before adding further acid.
• Carbon dioxide gas can also be used to decrease pH and can be injected automatically.
• Hydrochloric acid and sodium bisulphate should be diluted according to the manufacturer’s instructions when dispensed via automatic dosing equipment. Otherwise, a dilution of at least one in ten should be prepared before manually adding it to the pool water. Never add acid to the water body of the pool while it is in use.
Carbon dioxide is often used in preference to acid to lower pH. For safe handling, always add acid to water when making a dilution and use personal protective equipment.
• Before adjusting pH, ensure the total alkalinity is appropriate and stable. If pH is not corrected by setting the total alkalinity level, it can be further raised by the addition of more sodium bicarbonate (pH 8.2). However, this will cause a further increase in alkalinity.
In most pools, pH can be effectively controlled by using sodium bicarbonate without increasing alkalinity excessively. Sodium carbonate, also known as soda ash (pH 12.1) is sometimes used but is more dangerous to handle than sodium bicarbonate and contributes to scale formation. The addition of sodium hydroxide, also known as caustic soda (pH 14) to correct pH will cause high pH problems and should not be use.
Increase Calcium Hardness
• Add 110 g of calcium chloride, or 140 g of calcium sulphate, per 10,000 L of pool water to increase calcium hardness by 10 ppm.
If calcium hardness is consistently too low, consider using calcium-based disinfectants.
Decrease Calcium Hardness
• Dilution of pool water is the only practical way of lowering calcium hardness. If calcium hardness is high, disinfectants containing calcium should be substituted with those containing sodium.
To Lower Total Dissolved Solids (TDS)
• Dilute pool water usually by backwashing and refilling with fresh water. Regular dilution according to bather loading and backwashing should eliminate high, unaccounted-for TDS from occurring.